Blood: River of Life Flashcards
What is Blood?
- Fluid connective tissue that circulates continually around the body
- Transport system
Functions of Blood: Transport
- Nutrients to cells
- Dissolved gasses, oxygen and carbon dioxide
- Fat from stores to cells of the body
- Metabolic waste for elimination via the lungs (e.g. CO2) or kidneys (e.g. urea)
- Hormones (and drugs) from their origin (or administration) to their sites of action
Functions of Blood: Homeostasis
- Regulates body temperature
- Regulates pH (buffers, e.g. bicarbonate buffer system)
- Helps regulate the circulating blood volumes due to the osmotic pull of its plasma proteins
Functions of Blood: Defence
- Against infection, since it contains many components of our immune system
- Clotting factors preventing excessive blood loss
What is Blood Made Of?
- 55% plasma
- 45% formed elements - erythrocytes, leukocytes and platelets
Plasma Proteins
Mostly produced by the liver.
What are they?
- 60% albumin: maintain osmotic pressure and carrier molecule for free fatty acids, some drugs, and steroid hormones
- 35% globulins: antibodies and transport proteins
- 4% clotting factors: fibrinogen
- 1% regulatory: enzymes and hormones
Hemopoiesis or Haematopoiesis
The production of blood cells and platelets.
Occurs in:
- Red bone marrow which is found in flat and irregular bones and at the end of long bones
- Fatty yellow marrow no longer produces blood cells
Erythrocytes: Structure and Function
Transports respiratory gases.
Structure underlies function:
- Biconcave disc huge SA:V for gas exchange
- No organelles
- Haemoglobin for gas transport
- Flexible - can squash down when going through tiny capillaries
Erythrocytes: Fate
- Severe mechanical stresses
- Wear out with 100-120 day lifespan
- Haemoglobin is broken down into haem and globin.
- Globin: broken down into amino acids and released into the bloodstream
- Haem: iron is recycled to make new haemoglobin and the rest is excreted
Erythropoiesis
Production of RBCs from precursor stem cells. Dietary requirements: - Amino acids for globin production - Folic acid and VB12 for DNA synthesis - Iron for haem
Erythropoiesis: Formation of RBCs
- Starts as a stem cell
- Developmental stage:
- Phase 1: ribosome synthesis
- Phase 2: haemoglobin accumulation
- Phase 3: Ejection of the nucleus
- Erythrocyte!
Adjustment of Rate of Erythropoiesis
Hormone EPO, which acts on the bone marrow to stimulate erythropoiesis:
- Kidneys naturally produce EPO
- Hypoxia stimulates the kidneys to produce EPO
Leukocytes
White blood cells make up less than 1% of total blood volume.
Provide defence against infection, other foreign bodies, and our own cells when they go rogue.
Leukocyte rolling is when the WBCs leave the bloodstream and move to the site of infection.
Granulocytes: Neutrophils
- 40-75% of leukocytes
- Polymorphonuclear leukocytes
- Very active against bacteria
- Signal for back-up
- Lifespan of 30mins-10hrs
Granulocytes: Eosinophils
- 1-6% of leukocytes
- Found at the site of allergic reactions (airways, skin)
- Digest parasitic worms that are too large to be phagocytosed
- Modulators of the immune system - help reduce inflammation
Granulocytes: Basophils
- 1% of leukocytes
- Large granules take up basic dye
- Release histamine (attracts other leukocytes to site)
- Localised inflammation
Agranulocytes: Lymphocytes
- 20-50%
- Mostly lymphatic system
- Crucial to specific immunity
- Three types:
> T cells - active against virus-infected tumor cells
> B cells - antibody production
> Natural killer cells - cytotoxic
Agranulocytes: Monocytes
- 2-10%
- Once in blood, monocytes, when they leave circulation, macrophages
- Actively motile and phagocytic - crucial against viruses, intracellular bacterial parasites, and chronic infections
Platelets
Cell fragments with no nucleus but lots of granules, lysosomes, and mitochondria.
Vital for blood clotting.
Haemostasis: Vascular Spasm
- Vasoconstriction by damaged blood vessel
- Triggers include
> Direct injury
> Chemicals released by damaged vessel walls and by platelets
> Pain reflexes
Haemostasis: Platelet Plug Formation
- Rapid positive feedback loop
- A site of blood vessel injury, platelets stick to exposed collagen fibres
- They swell, become spiked and sticky, and release chemical messengers to attract more platelets
Platelets form a temporary plug that helps seal the blood vessels
Haemostasis: Coagulation
- Complex set of reactions
- Positive feedback
- Transformation of blood from a liquid to a gel
- Reinforces the platelet plug with fibrin threads
- Two pathways:
> Extrinsic pathway - tissue factor
> Intrinsic pathway - contact activation
Fibrinogen
A soluble protein which is converted into fibrin during blood clot formation.
Fibrin
An insoluble protein formed from fibrinogen during the clotting of the blood.
Thrombin
An enzyme in blood plasma which causes the clotting of blood by converting fibrinogen into fibrin.
Clot Retraction
Actin and myosin in platelets contract within 30-60mins.
Clot Repair
- Platelet-derived growth factor (PDGF) stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall
- Vascular endothelial (VEGF) stimulates endothelial cells to multiply and restore the endothelial lining
Fibrinolysis
- Begins within 2 days
- Plasminogen within clot is converted to plasmin
- Plasmin is a fibrin-digesting enzyme
- Plasmin breaks down clots
Erythrocyte Disorders: Anaemia
- Blood has a lower than normal number of RBCs or a lower than normal amount of haemoglobin in each RBS
- Most common cause is poor diet low in iron, VB12 or folic acid
- Also heavy periods
Leukocytes Disorders: Leucocytosis
- Increased leukocyte count
- Moderate may be due to inflammation or infection
- Severe may be due to marrow abnormality
Leukocyte Disorders: Leukopenia
- Decreased leukocyte count
- Can be caused by chemotherapy, radiation, overwhelming infection
Leukocyte Disorders: Leukemia
- Bone marrow occupied by cancerous leukocytes
- Immature, non-functional WBCs in the bloodstream
- Death caused by internal haemorrhage and overwhelming infections
- Treatments include: irradiation, cytotoxic drugs and stem cell transplants
Platelet Disorders: Thrombocytopenia
- Decreased platelet numbers
- results in bleeding - not enough platelets, can’t plug the hole
Platelet Disorders: Thrombocytosis
- Increased platelet number
- Results in clotting with blood vessels
Haematocrit
- Percentage of whole blood occupied by RBCs (45%)
- The remaining formed elements make up the thin buffy coat layer
- Normal values:
> Males: 40-50%
> Females: 37-47%
Differential White Cell Count
- Assesses the ability of the body to respond to and fight infection
- Detects the severity of allergic reactions, parasitic and other types of infection, or some drug reactions
- identifies some types of leukemia or lymphoma
